Can i use my External hardrive as a OS

I have a realy bad computer 4gb hardrive with a ancient motherboard dont care what it is dont even want to look! It has 256gb ram a 1.6ghz single core proscessor man this computer sucks, but anyway even with the most basic information on this computer it limits me just having it. I cant add any programs i cant do anything:

I want to know is their anyway that you can use a external hardrive as a operating system instead of using a IDE hardrive or any internal hardrive and use my external hardvie via USB with all uploaded files from my 4gb IDE drive copyed to my external hardvie instead?

So what your tellming is it wont feed off usb directly it needs to have a IDE OR SATA attacted to it. But isnt their something you can buy that converts a external drive from USB to SATA? If so would that be sufficent enough to use the external drive to be a primary OS